CVE-2025-61927

EUVD-2025-33777 · Published Oct 10, 2025

Happy DOM: VM Context Escape can lead to Remote Code Execution

Escape of VM Context gives access to process level functionality

Summary

Happy DOM v19 and lower contains a security vulnerability that puts the owner system at the risk of RCE (Remote Code Execution) attacks.

A Node.js VM Context is not an isolated environment, and if the user runs untrusted JavaScript code within the Happy DOM VM Context, it may escape the VM and get access to process level functionality.

It seems like what the attacker can get control over depends on if the process is using ESM or CommonJS. With CommonJS the attacker can get hold of the require() function to import modules.

Happy DOM has JavaScript evaluation enabled by default. This may not be obvious to the consumer of Happy DOM and can potentially put the user at risk if untrusted code is executed within the environment.

Reproduce

CommonJS (Possible to get hold of require)

const { Window } = require('happy-dom');
const window = new Window({ console });

window.document.write(`
  <script>
     const process = this.constructor.constructor('return process')();
     const require = process.mainModule.require;
  
     console.log('Files:', require('fs').readdirSync('.').slice(0,3));
  </script>
`);

ESM (Not possible to get hold of import or require)

const { Window } = require('happy-dom');
const window = new Window({ console });

window.document.write(`
  <script>
     const process = this.constructor.constructor('return process')();
  
     console.log('PID:', process.pid);
  </script>
`);

Potential Impact

Server-Side Rendering (SSR)

const { Window } = require('happy-dom');
const window = new Window();
window.document.innerHTML = userControlledHTML;

Testing Frameworks

Any test suite using Happy-DOM with untrusted content may be at risk

Attack Scenarios

Data Exfiltration: Access to environment variables, configuration files, secrets
Lateral Movement: Network access for connecting to internal systems. Happy DOM already gives access to the network by fetch, but has protections in place (such as CORS and header validation etc.).
Code Execution: Child process access for running arbitrary commands
Persistence: File system access

Recommended Immediate Actions

Update Happy DOM to v20 or above
- This version has JavaScript evaluation disabled by default
- This version will output a warning if JavaScript is enabled in an insecure environment
Run Node.js with the "--disallow-code-generation-from-strings" if you need JavaScript evaluation enabled
- This makes sure that evaluation can't be used at process level to escape the VM
- eval() and Function() can still be used within the Happy DOM VM without any known security risk
- Happy DOM v20 and above will output a warning if this flag is not in use
If you can't update Happy DOM right now, it's recommended to disable JavaScript evaluation, unless you completely trust the content within the environment

Technical Root Cause

All classes and functions inherit from Function. By walking the constructor chain it's possible to get hold of Function at process level. As Function can evaluate code from strings, it's possible to execute code at process level.

Running Node with the "--disallow-code-generation-from-strings" flag protects against this.

Technologies

Happy-Dom Happy-Dom

Weaknesses

CWE-94

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Stealth

T1027.006HTML Smuggling T1027.009Embedded Payloads T1564.009Resource Forking

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.